The invention relates generally to roaming in a wireless communication network. More particularly, the invention relates to controlling roaming in a geographic area in which there are multiple service providers.
Mobile stations (e.g. wireless telephones) operate within a wireless communication network by establishing communication with base stations. These base stations generally comprise antennas and the required radio and control equipment necessary for such communication. These base stations are connected to mobile switching centers which control the operation of the base stations. The mobile switching centers may further be connected to other communication networks, such as the public switched telephone network (PSTN), the Internet, other wireless communication networks, or other types of communication networks. The architecture of such wireless communication networks is well known.
Each base station serves a geographic area called a cell. Thus, when a mobile station is operating within a given cell it establishes communication with the base station serving that cell. As a mobile station moves about the geographic coverage area of the wireless network, it may be necessary to establish communication with various base stations. For example, during a voice call, a mobile station may leave the current serving cell and enter an adjacent cell. In order for the voice call to continue uninterrupted, it is necessary to transfer communication from a voice channel of the current serving cell base station to a voice channel of the base station of the adjacent cell into which the mobile station is moving. Such a procedure is called a handoff and is well known in the art of mobile wireless communications.
When a mobile station is turned on and registered with the wireless network, but not actively being used for a voice call, the mobile station is in communication with the serving base station via that base station""s control channel. When a mobile station is communicating with a control channel, the mobile station is said to be xe2x80x9ccamped onxe2x80x9dto the control channel. It is via this control channel that the base station can notify the mobile station that communication is requested (e.g. there is an incoming telephone call for the mobile station). It is also via this control channel that a mobile station can notify the base station that communication is requested (e.g. the mobile station requests a voice channel for an outgoing telephone call).
In a manner similar to that described above with respect to voice calls, when the mobile station is registered but not currently being used for communication, the mobile station may be moving about the coverage area of the wireless communication network.
In order for the mobile station to remain actively registered with the wireless communication network, it is necessary to transfer communication from the control channel of the current serving cell base station to the control channel of the base station of the adjacent cell into which the mobile station is moving. Such a procedure is called reselection and is well known in the art of mobile wireless communications.
In the current wireless communications environment, it is common for there to be multiple service providers providing wireless communication services within the same geographic area. When a subscriber subscribes for wireless service with a service. provider, that service provider is the primary service provider for that subscriber""s mobile station. Thus, when the subscriber""s mobile station is operating in a geographic area in which the primary service provider and some other service provider (i.e. a secondary service provider) both provide wireless services, it is preferable for the mobile station to use the primary service provider for service. If, however, the mobile station is operating in an area in which the primary service provider does not provide service, it may be desirable for the mobile station to obtain service from some secondary service provider. When a mobile station obtains service from a service provider other than its primary service provider, that mobile station is roaming. The roaming process is controlled by the mobile station""s control processor executing program code which implements the desired roaming algorithms.
Currently, there are many geographic areas in which the coverage area of multiple wireless service providers overlap. Consider the geographic area shown in FIG. 1 which is served, at least in part, by two service providers, A and B. Assume that service provider A is the primary service provider for a particular mobile station and that service provider B is a secondary service provider for the mobile station. This is a common situation where, for example, coverage area 102 is a densely populated urban area, and coverage area 104 is a somewhat less populated suburban area. In this case, secondary service provider has base stations (indicated in FIG. 1 with a B) throughout both coverage areas 102 and 104, while primary service provider A only has base stations (indicated in FIG. 1 with an A) in the more densely populated coverage area 102. In such a situation, service provider A will generally have an agreement with service provider B such that service provider A""s subscribers can obtain service from service provider B while roaming in coverage area 104. However, when such a subscriber is within coverage area 102, the mobile station should register with service provider A base stations.
A problem with mobile station roaming exists where there are coverage holes in the coverage area 102 with respect to service provider A. A coverage hole is an area within the serving area of the service provider in which a mobile station cannot receive acceptable service from the service provider. Coverage holes may exist for various reasons. For example, there may be a geographic area which, because of terrain and base station antenna locations, cannot receive sufficiently strong signals for service (e.g. a geographic coverage hole). Other coverage holes may exist because of buildings, for example parking garages. Another example of a coverage hole may be an elevator. When a mobile station moves into a coverage hole, it is often the case that the mobile station will emerge from the coverage hole within a short period of time.
The problem with coverage holes in multiple service provider environments is illustrated by the following example in conjunction with FIG. 1. Consider a service provider A coverage hole 106 within coverage area 102. Assume this is a geographic coverage hole, such that when a mobile station enters this coverage hole 106, the mobile station will emerge from the coverage hole within one minute. However, because of the roaming procedures the mobile station follows, when the mobile station detects that it can no longer receive service from primary service provider A, it will initiate its roaming process. Assuming that coverage hole 106 is only a coverage hole for service provider A, and not for service provider B, then the mobile station will reselect to a control channel of a service provider B base station and thus the mobile station will now be registered with service provider B. This is an undesirable result for several reasons.
When a mobile station is registered with a service provider, a display on the mobile station will identify the service provider providing the service. Thus, when a mobile station is registered with service provider A in coverage area 102, the display will read, for example, xe2x80x94Home Areaxe2x80x94Service Provider Axe2x80x94. When the mobile station is registered with service provider B in coverage area 104, the display will read, for example, xe2x80x94Extended Areaxe2x80x94Service Provider Bxe2x80x94. In these two situations, the display would be as expected by the subscriber. However, if the mobile station enters coverage hole 106 and reselects to service provider B, the display will change to readxe2x80x94Extended Areaxe2x80x94Service Provider Bxe2x80x94. This may be confusing to the subscriber because the subscriber thinks he/she is still within the primary service provider area. Further, some of the features, which the subscriber expects to receive while in coverage area 102, will not be available to the subscriber while registered with service provider B. Also, the quality of the service provided will be beyond the control of the primary service provider A.
Thus, a solution to this problem would benefit both service providers and subscribers.
In view of the problems discussed above, it has been recognized that it is preferable that a mobile station which enters a coverage hole within the coverage area of the mobile station""s primary service provider be temporarily without service, rather than the mobile station reselecting to a secondary service provider. In accordance with the invention, when a mobile station determines that acceptable service is no longer available from the primary service provider, it will only reselect to a secondary service provider if the mobile station is on the periphery of the coverage area of the primary service provider. If the mobile station is not on the periphery of the coverage area of the primary service provider, then it is assumed that the mobile station has entered a coverage hole and the mobile station will be prevented from reselecting to a secondary service provider a time period. This will allow the mobile station sufficient time to emerge from the coverage hole.
In accordance with one embodiment of the invention, the mobile station determines whether it is at the periphery of the primary service provider coverage area by examining the neighbor list of control channels being transmitted by the current serving base station. If the neighbor list of the current serving base station contains only identifications of the primary service provider control channels, then a determination is made that the mobile station is operating in the interior of the primary service provider coverage area. Alternatively, if the neighbor list of the current serving base station contains at least one identification of a non-primary service provider control channel, then a determination is made that the mobile station is operating on the periphery of the primary service provider coverage area.
In other embodiments, the mobile station determines whether it is at the periphery of the primary service provider coverage area by analyzing other information sent from the serving base station. Such information can include the cell identification transmitted by the base station, or other indicia indicating whether the cell is a periphery cell.
These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings.